This invention relates to seam welders. Typically these machines have confronting wheel electrodes between which the work passes. One electrode is bodily movable toward the other and must be loaded to develop the desired pressure or load on the work. A critical part of any welding operation is the follow-up as the metal melts -- i.e. during the forging part of the weld cycle. The movable electrode wheel assembly includes a ram and bearings and the weight of the assembly becomes appreciable, . . . for example, in two typical machines manufactured by applicant's assignee the assembly weighs 135 Kg and 208 Kg. Considering that the electrode desirably moves 0.25 mm to 0.5 mm during the follow-up phase, the force required to move the assembly in a short weld cycle (1/2 to 1 cycle of 60 Hz) becomes very high -- 27 to 218 Kg in the case of the 135 Kg assembly and 42 to 338 Kg in the case of the 208 Kg assembly (ignoring friction in both cases). And then the electrode assembly must be stopped . . . preferably in one half the follow-up distance which means the work must absorb between 27 and 675 Kg depending upon the assembly and distance involved. With such forces involved the use of seam welders is limited and in some applications results in deformation of the work which is accepted in the interest of economy even though the function of the efficacy of the end product may be adversely affected.
There have been attempts to improve the design of the wheel electrode by providing some resiliency to the electrode wheel. Russell U.S. Pat. No. 2,918,546 shows a spring loaded wheel which can be loaded to a predetermined maximum. While he does not speak of follow-up, there may be some in his design. He uses two springs arranged in such a way that the actual loading obtained is dependent upon the angular position of the wheel. Current is delivered to the wheel through the springs (and the drive gearing) and there is always a question of developing spring harmonics in rapid welding. His arrangement may be satisfactory for very light hand held work as he describes but clearly cannot be applied to heavy duty use simply because the welding current would melt the springs. Caputo U.S. Pat. Nos. 2,205,680 and 2,276,925 disclose a resiliently mounted eccentric wheel for applying the welding current to the work. There is a pressure applying wheel on each side of the electrode wheel. Thus he has increased the mass (weight) by attempting to separate the pressure and current sources. This is obviously counter productive.